Make landing page responsive on mobile

[shelabastida933-pixel]

Summary

• Add a mobile hamburger menu so the landing page nav does not crowd small screens.
• Tighten mobile spacing, text widths, and CTA layout to avoid clipping and horizontal overflow.
• Stack the tools grid, CTA buttons, and footer cleanly on phone widths while preserving desktop layout.

Validation

• npm run build
• npx eslint src/pages/LandingPage.tsx
• Visual screenshots checked at 320x568, 375x812, and 414x896 using a production Vite preview.

Closes #3